Record rainfall has depleted soil nutrients in Southeast

Clemson University Peanut Specialist Scott Monfort held up a peanut plant at a recent South Carolina field day and asked growers what caused the obvious demise of the plant.

With all the historic rainfall occurring in the state, the options for answers were nearly limitless, but in this case it was potash deficiency.

A lack of potassium is almost unheard of in Southeast peanut production, and Monfort explained that this occurrence was rare this year in South Carolina.

However, such a rare deficiency is characteristic of nutrient losses that have shown up across the Southeast in the wake of what many are calling a 100-year rainfall.

From the Florida Panhandle to the Northern Neck of Virginia people have suffered through what is proving to be a once-in-a-lifetime occurrence for farmers in the region.

Some areas, like the Piedmont Region of North Carolina and Low Country Region of South Carolina seem to have been especially hard hit.

Clemson University Extension Ag Agent Charles Davis says one thing for sure is that farmers better soil sample more thoroughly than ever, because this past year has depleted soils of nutrients more than ever.

Rainfall in most of North Carolina has been at record high levels from early spring through summer, with some areas receiving more than 30 inches. As a result, most crops have struggled due to poorly developed root systems.

Agronomists warn that the growth of upcoming crops is also likely to be affected unless soil-nutrient reserves are monitored and replenished.

Soil sampling a critical issue

David Hardy, chief of the Soil Testing Section with the North Carolina Department of Agriculture and Consumer Services, and Carl Crozier, soil science professor and extension specialist at North Carolina State University, urge growers to be particularly vigilant about soil sampling this summer and fall.

“And some of our nutrients are what we call ‘mobile in soils,’ simply meaning they move with excessive water through the soil. Farmers are more familiar with the term ‘leaching.’

“Potassium, nitrogen and sulfur are the most mobile nutrients,” Hardy says, “but even nutrients such as magnesium, which is held more tightly than potassium, can be depleted due to excessive rainfall.

“This year growers across the state really need to check the nutrient status of soils by soil testing.”

In some areas of the Piedmont Region of North Carolina, growers have been dealing with flooded fields since April.

Though spring months were more soggy, continuous heavy rainfall throughout the growing season has left many fields constantly wet for long periods of time. Soggy isn’t a scientific term, but Crozier says it can cause real problems with plant nutrients.

“Poorly drained soils may have been flooded for long periods,” he says.

“The problem in areas where water has been standing is more likely to be denitrification than leaching. In that case, nitrogen is lost as a gas to the air.

“Growers need to remember that routine soil testing does not measure soil nitrogen levels. The nitrogen recommendations given on a soil-test report represent the typical needs of the crop and do not take into account that residual nitrogen levels might be even lower than expected given the weather this past season,” he explains.

Even soil pH levels that have been relatively stable for many years, even the lifetime of some growers, may be knocked out of kilter by the heavy rainfalls.

“On especially sandy soils, I expect there may have been considerable changes in pH over the past four to five months,” Hardy says.

“If a field was borderline in needing lime last year and none was applied, it definitely needs to be tested this year.

Testing not an option

“This was one of the wettest growing seasons I can remember. Growers whose crops drowned or rotted may want to forget this past season, but they need to let it remind them that soil testing in the coming months is not optional,” he says.

The prolonged wet weather and cool temperatures combined to create big production problems on most crops staple to the Southeast. The unusual weather also took a toll on the soil, both directly and indirectly.

Thousands of acres of cropland were abandoned this spring and summer and the high cost of replacing nutrients depleted by excessive rainfall wasn’t offset by the necessities of adding nutrients for crops, because in many cases, no crop was left in the field.

Wheat is in short supply globally and in big demand in the Southeast for livestock feed. The latter demand doesn’t come with the same high prices as does wheat for human consumptions.

The result may be a reduction of input costs by growers, which could equate to a reduction in much needed soil nutrients.

Crozier says growers planning to plant small grains this fall are especially urged to sample ahead of that crop. The sooner samples are submitted, the sooner recommendations can be implemented to get the crop started off with the best fertility possible.

In North Carolina, for samples received until mid-November, soil test results are free and the turnaround time is generally two weeks.

Micronutrient losses in crops have been especially widespread across the Southeast this year — yet another potential risk to growers and possibly to humans.

Zinc deficiencies in particular have cropped up in places where they don’t typically occur — in most cases where record rainfall has occurred.

Zinc deficiency is well documented in crops, but little is known about the correlation between low zinc levels in crops and low zinc levels in humans.

Impact on humans

If we are indeed what we eat, then humans, too, need to be aware of the impacts of the depletion of nutrients from the soil and how this correlates to humans who consume these crops.

Zinc is an essential micronutrient needed by crops and people. According to the United Nations, almost half of the world’s cereal crops are deficient in zinc, leading to poor crop yields.

Medical research has shown that areas with zinc-deficient soils are often regions with widespread zinc deficiency in humans.

In fact, one-third of the world population is at risk of zinc deficiency, ranging dramatically from less than five percent to near 75 percent, depending on the country.

Zinc deficiency is the fifth leading risk factor for disease in the developing world.

Wheat growers are already seeing the effect of the loss of nutrients in many fields across the Upper Southeast. Many of the nutrients and micronutrients that are normally available in the soil just aren’t there this year.

As growers begin planning for their 2014 crops, soil testing should be a renewed area of interest.

Many of the unusual disease problems seen this year were likely physiological and heavily impacted by the loss of vital nutrients from excessive rains.

Providing adequate nutrition for next year’s crop is going to be a vital factor in how well spring crops get up and growing next season.